Charge initiated lightning protection system for a wind turbine blade and wind turbine blade with the charge initiated lighting protection system

ABSTRACT

A lightning protection system is provided for a wind turbine blade via charge initiation (Charge Initiated Lightning Protection). The lightning protection system includes at least one electric charge generator for generating electric charge at a lightning receptor of the wind turbine blade such that an electrostatic field is generated at the lightning receptor leading lightning current directly to the lightning receptor. Additionally a wind turbine blade having at least one such lightning protection system is provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a lightning protection system for a windturbine blade and a wind turbine blade with the lighting protectionsystem.

2. Description of the Related Art

A blade material of a wind turbine blade, e.g. GFRP (Glass FiberReinforced Polymer), can be destroyed by a lightning stroke (e.g.composed by a leader and a return stroke). Therefore a wind turbineblade usually has a lightning protection system.

The lightning protection system consists of lightning receptors at ablade surface of the blade. Inside the blade there are conductors withelectrically conducting material connected to the receptors. Via theconductors lightning current which is caused by a direct lightningstroke into the receptors can be diverted.

An area of the receptors is limited leading to a relatively small safecontact surface for the lightning stroke (few square centimeters)compared to the whole blade surface (e.g. 100 square meters). Due tothat fact a probability for a direct lightning stroke into the lightningreceptors is relatively low. As a consequence a puncture of the bladematerial caused by a lightning stroke into the blade surface cannot beavoided.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an efficient and reliablelightning protection system for a wind turbine blade. A puncture of thewind turbine blade caused by a direct lightning stroke into the he bladesurface should be avoided.

Another object of the invention is the providing of a wind turbine bladewith such an efficient and reliable lightning protection system.

These objects are achieved by the invention specified in the claims.

BRIEF DESCRIPTION OF THE INVENTION

The invention provides a lightning protection system for a wind turbineblade via charge initiation (Charge Initiated Lightning Protection,CILP). The lightning protection system comprises at least one electriccharge generator for generating electric charge at a lightning receptorof the wind turbine blade such that an electrostatic field is generatedat the lightning receptor leading lightning current directly to thelightning receptor.

Additionally the invention provides a wind turbine blade having at leastone such lightning protection system. Two or more such lightningprotection systems are possible, too.

The charge generator has the function of localization and concentrationof electric charge at the lightning receptor. By that a receptor surfacecharge of the lightning receptor is changed. This leads to anelectrostatic field which gives a preferential path for the current of alightning stroke via the lightning receptor and via the connectorsinside the blade. As a result the probability of a damage of the bladesurface of the wind turbine blade is reduced.

The charge can actively be produced or located. Therefore a specialdevice for the separation of charge is used. For instance this device isa source of electric charge like a battery.

In a preferred embodiment the electric charge generator is developedsuch that the electric charge is passively generated. The electriccharge is passively produced. No additional device for generating thecharge is necessary.

In a further preferred embodiment the electric charge can be passivelygenerated by rotating the wind turbine blade. For instance the bladematerial is a dielectric material like GFRP. The receptor material ofthe lightning receptor is a metal like copper. Due to free charge in theair the blade surface of the blade is charged. The blade surface chargeof the blade surface causes the charging of the lightning receptor. Forinstance the blade surface is negatively charged. Negative charge islocated on the blade surface of the blade.

Consequently the receptor with the metal as receptor material ispositively charged. This leads to a relatively high amount of positivecharge at the receptor. An electrostatic field is built up which isleading the current of a lightning stoke directly to the lightningreceptor.

Various designs of the lightning receptor are possible. E.g. thelightning receptor can be made of one metallic piece. Alternatively thelightning receptor consists of two or more pieces. E.g. the lightingreceptor has an inner core with core material and at least one outerring with ring material surrounding the inner ring. Two or more outerrings are possible, too. The core material and/or the ring material areelectrically conductive material, e.g. metals. In the case bothmaterials are conductive materials the inner core and the outer ring arepreferably separated from each other by an inter layer with electricallyinsulating inter layer material. Between two adjacent outer rings withelectrically conductive materials an interlayer with electricallyinsulating materials is arranged, too. But the interlayer can be leaved.The core and the surrounding ring and adjacent rings respectively aredirectly connected to each other.

In summary following advantages are connected with the invention:

-   -   The Charge Initiated Lightning Protection system is an efficient        and easy way for protecting a wind turbine blade from the effect        of a lightning stroke.    -   Just by rotating the wind turbine blade electric charge can be        concentrated at the lightning receptor guiding the lightning        current and avoiding the puncture of the blade surface of the        wind turbine blade as a result of a lightning stroke.    -   Additional devices for guiding the lightning current, e.g.        metallic strips on the blade surface of the wind turbine blade        are not necessary. Such additional devices could negatively        affect a characteristic of the wind turbine blade, e.g. a mass        of the wind turbine blade and a fluid flow of the wind turbine        blade.

BRIEF DESCRIPTION OF THE DRAWING

Further features and advantages of the invention are disclosed by thedescription of an exemplary embodiment with reference to the drawing.FIG. 1 shows a detail of an example of a blade surface of a wind turbineblade equipped with the charge initiated lighting protection system.

DETAILED DESCRIPTION OF THE INVENTION

Given is a wind turbine blade 1. The blade material of the wind, turbineblade is GFRP.

The wind turbine blade 1 has a charge initiated lightning protectionsystem 2. This lightning protection system 2 comprises a lightingreceptor 21 which is integrated into the wind turbine blade 1. Areceptor surface 211 of the lightning receptor 21 and a blade surface101 of the wind turbine blade 1 are flushed with each other.

The lightning receptor 21 is made out of one piece and comprises a metalas receptor material. The lightning receptor 21 is connected to (notshown) inner conductors with conductive material of the blade 1.

In a not shown embodiment the receptor 21 comprises one inner core andone outer ring surrounding the inner core. The ring and the corecomprise electrically conductive material. The ring and the core areseparated from each other by an interlayer with electrically insulatingmaterial. This electrically insulating material is GFRP.

The lighting protection system 2 additionally comprises at least oneelectric charge generator 20. The electric charge generator 20 isdeveloped such that the electric charge is generated passively: Byrotating the wind turbine blade negative electric charge at the bladesurface 101 of the wind turbine blade 1 is passively generated. Negativeelectric charge is concentrated at the blade surface 101. The negativelycharging of the blade surface 101 of the wind turbine blade 1 causes apositively charging of the lightning receptor 21 and at the lightningreceptor surface 211 of the lightning receptor 21 respectively. Positivecharge is located at the receptor surface of the lightning receptor.Hence an electrostatic field is built up. This electrostatic fieldguides a lightning stroke. The lightning current of the lightning strokecan be diverted via the lightning receptor and via the connectors insidethe blade. As a result the probability of a damage of the blade surfaceof the wind turbine blade by a lightning stroke is reduced.

1-4. (canceled)
 5. A lightning protection system for a wind turbineblade, the lightning protection system comprising: an electric chargegenerator for generating an electric charge at a lightning receptor ofthe wind turbine blade such that an electrostatic field is generated atthe lightning receptor leading lightning directly to the lightningreceptor.
 6. The lightning protection system according claim 5, whereinthe electric charge generator is configured such that the electriccharge is generated passively.
 7. The lightning protection systemaccording claim 6, wherein the electric charge is generated by rotatingthe wind turbine blade.
 8. A wind turbine blade, comprising: a lightningprotection system according to claim
 5. 9. The wind turbine bladeaccording to claim 8, wherein the electric charge generator isconfigured such that the electric charge is generated passively.
 10. Thewind turbine blade according to claim 8, wherein the electric charge isgenerated by rotating the wind turbine blade.